Observer-based robust controller design and realization of a gantry stage

A precise positioning operation is typically required for gantry systems in applications such as drop-on-demand (DOD) printing processes, precision metrology, and circuit assembly. This work presents experimental results from studies of a disturbance observer (DOB) based variable structure controller (VSC) for a gantry stage. For DOB-based controllers, a nominal model is needed; however, obtaining the nominal model is difficult for systems with friction. A pseudo-random binary signal (PRBS) is utilized to identify the linear nominal model of the gantry stage with friction. To compensate for friction effects, a filtered-VSC is studied to increase robustness and compensate for modeling uncertainties and external disturbances. Experimental results demonstrate the effectiveness of the proposed robust control structure.